About Area Calculator
Area Calculator is a free, browser-based tool for measuring areas and distances on any image. Whether you are working with maps, floor plans, aerial photos, satellite imagery, or site plans, simply upload your image, set the scale, and start drawing polygons. Area and perimeter are calculated instantly.
I built this tool because I could not find a free, simple, and private alternative. Existing options were either paywalled, cluttered with upsells, or required you to upload your files to a third-party server. Area Calculator runs entirely in your browser — your images never leave your device — and it will remain free to use indefinitely.
How It Works
- Upload an image — Drag and drop or click to browse. Supports PNG, JPG, WebP, and PDF formats. For PDFs, a page picker lets you choose which page to measure.
- Set the scale — Select the Scale tool, then click two points on the image whose real-world distance you already know (the ends of a dimension line, a scale bar, or two known landmarks). Enter that distance and the tool calculates the pixel-to-real-world ratio. All subsequent measurements use this calibration.
- Draw shapes — Select the Draw tool and click to place polygon vertices around the area you want to measure. Click the first vertex again (or double-click) to close the shape. You can draw any number of shapes on the same image, each colour-coded automatically.
- Get results — Area and perimeter appear instantly in the sidebar as you draw. Switch between units at any time without redrawing. Export your results as a PNG image, a PDF report, a CSV spreadsheet, or copy them to the clipboard.
What You Can Measure
Area Calculator works with any top-down or near-orthographic image. Here are the most common use cases:
- Floor plans — Measure individual rooms, combined living areas, or total floor area from architectural drawings. Instantly switch between square metres and square feet.
- Land and property — Trace plot boundaries on a cadastral plan or satellite image to estimate parcel area for conveyancing, planning, or listing purposes.
- Agriculture — Outline fields, paddocks, or orchards on aerial imagery to calculate crop area, plan irrigation, or estimate input quantities per hectare or acre.
- Roofing and construction — Measure roof faces, decking, or building footprints from drone photographs or elevation drawings to estimate materials and cost.
- Ecology and environmental science — Delineate habitat patches, wetland extents, or survey plots on satellite imagery for environmental impact assessments.
- Urban planning — Quickly measure setbacks, green space ratios, car park footprints, or proposed building envelopes on site plans without specialist GIS software.
Tips for Accurate Measurements
- Use the longest possible reference distance. When setting the scale, choose two points that are as far apart as possible. A longer baseline reduces the proportional error caused by imprecise clicking.
- Zoom in before placing vertices. Use the scroll wheel or trackpad to zoom in on corners and edges before clicking. The tool supports sub-pixel vertex placement at high zoom levels.
- Stick to orthographic images. Perspective distortion in photographs taken at an angle will introduce error that no amount of careful clicking can correct. Use overhead drone shots, scanned plans, or satellite imagery where possible.
- Double-check your scale input. The biggest source of error is usually an incorrect reference distance. Verify the units and the value before drawing your shapes.
- Drag vertices to fine-tune. After closing a polygon, you can drag any vertex to adjust the boundary without starting over.
Key Features
- Draw any number of shapes on a single image, each with a unique colour and editable label
- Drag vertices to adjust polygon boundaries after drawing
- Zoom and pan for precision work on detailed or large images
- Distance tool for measuring point-to-point straight-line distances
- Unit selector: metres, kilometres, feet, yards, and miles (with automatic conversion to hectares and acres for large areas)
- Export as PNG (annotated image), PDF (image + measurements table), CSV (structured data), or plain text
- Save and load full project files (image + all shapes) as JSON
- Auto-save to browser storage — your last session is restored on the next visit
- Keyboard shortcuts for all tools and common actions
- Dark mode support
- Works entirely in your browser — no data is ever uploaded to a server
Frequently Asked Questions
- Is this tool really free?
- Yes. Area Calculator is free with no usage limits, no account required, and no premium tier. It is supported by unobtrusive advertising.
- Do my images stay private?
- Completely. The tool runs client-side using the HTML5 Canvas API. Images are read directly from your disk into your browser's memory and are never transmitted over the network. See the Privacy Policy for full details.
- How accurate is it?
- For a well-calibrated scale and a polygon drawn carefully on an undistorted orthographic image, accuracy is typically within 1–2%. The main sources of error are an inaccurate scale reference, imprecise vertex placement, and lens or perspective distortion in the source image.
- Can I work with large files?
- Yes, though very large images (e.g. high-resolution drone ortho-mosaics) may be slow to load depending on your device's memory. There is no server-side file size limit because everything runs locally.
- Can I measure irregular shapes?
- Yes. You can place as many vertices as you need, so even highly irregular boundaries can be traced accurately. The more vertices you use, the closer the polygon follows the real boundary.
Privacy
All processing happens locally in your browser. Your images and measurements never leave your device. See our Privacy Policy for full details.